represents our jewel pin; we afterward cut away two-fifths and draw the
full line _D_, as shown. We show at Fig. 59 a portion of Fig. 58,
enlarged four times, to show certain portions of our delineations more
distinctly. If we give the subject a moment's consideration we will see
that the length of the prong _E_ of the lever fork is limited to such a
length as will allow the jewel pin _D_ to pass it.


HOW TO DELINEATE THE PRONGS OF A LEVER FORK.

[Illustration: Fig. 58]

[Illustration: Fig. 59]

To delineate this length, from _B_ as a center we sweep the short arc
_f_ so it passes through the outer angle _n_, Fig. 59, of the jewel pin.
This arc, carried across the jewel pin _D_, limits the length of the
opposite prong of the fork. The outer face of the prong of the fork can
be drawn as a line tangent to a circle drawn from _A_ as a center
through the angle _n_ of the jewel pin. Such a circle or arc is shown at
_o_, Figs. 58 and 59. There has been a good deal said as to whether the
outer edge of the prong of a fork should be straight or curved.

To the writer's mind, a straight-faced prong, like from _s_ to _m_, is
what is required for a fork with a single roller, while a fork with a
curved prong will be best adapted for a double roller. This subject will
be taken up again when we consider double-roller action. The extent or
length of the outer face of the prong is also an open subject, but as
there is but one factor of the problem of lever escapement construction
depending on it, when we name this and see this requirement satisfied we